Reservoir well production and testing involves drilling subsurface formations and monitoring various subsurface formation parameters. Drilling and monitoring typically involves using downhole tools having electric-power, mechanic-power, and/or hydraulic-power devices. To power downhole tools using hydraulic power, pump systems are used to pump hydraulic fluid. Pump systems may be configured to draw hydraulic fluid from a reservoir and pump the fluid to create a particular pressure and flow rate to provide necessary, hydraulic power. The pump systems can be controlled to vary output pressures and/or flow rates to meet the needs of particular applications. In some example implementations, pump systems may also be used to draw and pump formation fluid from subsurface formations. A downhole string (e.g., a drill string, a wireline string, etc.) may include one or more pump systems depending on the operations to be performed using the downhole string. Traditional pump systems are limited in their operation by the range of flow rates that can be achieved. Examples of pump systems for a downhole tool positionable in a wellbore penetrating a subterranean formation can be found in U.S. Patent Application Pub. Nos. 2005/0034871, 2006/0042793 and 2006/0168955. Other examples of pump systems for a downhole tool positionable in a wellbore penetrating a subterranean formation can be found in “New Dual-Probe Wireline Formation Testing and Sampling Tool Enables Real-Time Permeability, and Anisotropy Measurements”, SPE 59701, 21-23 Mar. 2000 by Proett and al. or in the brochure of the Reservoir Characterization Instrument (RCISM) commercialized by Baker Hughes, 2000.